Buying Japanese Currency in the UK

I'm thinking of making a visit to Japan in possibly a years time, for probably a month or so.

I was wondering, where can I buy Japanese currency in the UK?

I'm going to be buying quite a bit every month till I have a fair amount(My way of saving up for the trip).
So I only have the plane ticket cost to worry about :)

Thanks for any answers

It all depends where you live. In a small town your bank will not have Yen and will have to order them from London, for example, and charge a premium. If you are in London or have a chance to go there (or live in a very touristy town like Bath or York) a "bureau de change" is the best place to go to. Buying yen every so often is kind of problematic as the rate fluctuates. If you plan to go one year from now start tracking the yen rate and buy when they are low?! You need yen for your arrival but can also use a credit card to pay for hotels and can use a debit card from your bank (with the Maestro logo or Cirrus, Plus) to get cash at a ATM.

I was wondering, where can I buy Japanese currency in the UK?
Marks and Spencer's usually give you the most yen for your pounds compared to other exchange offices like the Royal Mail or banks.

Here at money saving expert, they tell you the best place to buy your yen:
http://travelmoney.moneysavingexpert.com/

You can compare between different places. I tried to get mine at tesco (since they usually have a good rate) but I ended up ordering it on the post office online. For some reason the exchange rate is slightly better online than in store.